3.5. CSS2 Units

In addition to what we've covered,
CSS2 adds a small
number of new units, almost all of which are concerned with
aural style
sheets (employed by those browsers that are capable of speech).
We'll briefly cover them here:

Angle values

Used to define
the position from which a given sound should seem to originate. There
are three type of angles: degrees (deg ), grads
(grad ), and radians (rad ).
For example, a right angle could be declared as
90deg, 100grad , or
1.57rad ; in each case, the values are translated
into degrees in the range
through 360. This is also true of negative values, which are allowed.
The measure -90deg is the same as
270deg.

Time values

Used to specify
delays between speaking elements, these values can be expressed as
either milliseconds (ms) or seconds
(s). Thus, 100ms and
0.1s are equivalent. Time values may not be
negative.

Frequency values

Used to
declare a given frequency for the sounds that speaking browsers can
produce. Frequency values can be expressed as hertz
(Hz) or megahertz (mHz) and
cannot be negative. The values labels are case-insensitive, so
10mHz and 10mhz are equivalent.

In addition to these values, there is also an old friend with a new
name. A URI is a Uniform Resource
Identifier, which is sort of another name for a Uniform
Resource Locator (URL). The difference is, for now, mostly semantic,
but many authors are beginning to adopt the convention of referring
to online addresses as URIs, not URLs. The specification still
requires that URIs be declared with the form
url(...), though, so it's hard to know
exactly what the point was of including a section in CSS2 about how
CSS2 uses URIs instead of URLs.